It is, as you'd expect, a weighty legal document which you may not find instantly digestible. A quick scan throws up a range of old constitutional familiars: the Claim of Right Act 1689, the Act of Union, the Sewel convention -- and even our old friend MacCormick v Lord Advocate. But what does all this mean? When you boil it all down, what is the Scottish Government really arguing for in the Brexit hearing?

In a nutshell, James Wolffe is pursuing two distinct lines of argument. The first focuses on whether ministers can use the royal prerogative to activate Article 50 and the United Kingdom's departure from the European Union. The second concerns the so-called "Sewel" convention. Is Holyrood's consent constitutionally necessary, if Article 50 is to be activated?

Let's start with the first line of argument. The royal prerogative is the name given to the residual legal powers of the crown. Its exercise entitles Her Majesty's government to enter treaties with foreign powers, or even to declare war, without reference to parliament. Earlier this year, the three judges of the Divisional Court held that Theresa May's government could not use the foreign affairs prerogative to activate Article 50. The Lord Chief held that Westminster must pass legislation, to begin disentangling Britain from the EU, and stripping away the rights in domestic law connected to it. The Scottish Government have weighed in behind this argument, but appeal to different sources.

The Lord Advocate invokes the preamble to the Claim of Right Act, passed by the old Scottish Parliament in 1689 in the aftermath of the eviction of King James VII and II from the country and the throne. Parliamentarians slammed James for having corrupted his rule "from a legall limited monarchy to ane Arbitrary Despotick power and in a publick proclamation asserted ane absolute power to cass annull and dissable all the lawes." Their 1689 Act states any attempt to use crown authority to "cass, annull and dissable" laws was itself "Contrair to Law."

Here, the 1706 and 1707 Acts of Union warrant a passing mention. As James Wolffe points out, Article XVIII of the Acts provides that "all other laws in use, within the Kingdom of Scotland, do after the union and notwithstandng thereof, remain in the same Force as before ... but alterable by the Parliament of Great-Britain." Notice the critical point here. "At the foundation of the United Kingdom, it was Parliament ... and not the Crown, which was given power to change the law of Scotland." Read together, he suggests, these sources confirm the Divisional Court's judgment that it is for parliament -- not the crown in exercise of its royal prerogatives -- to alter the law of the land.

Here the Scottish Government's argument shifts forwards, towards more contemporary sources. Wolffe argues that if Theresa May was entitled to use the prerogative to activate Article 50, its effect would hollow out a range of laws currently applicable in Scotland, including the Scotland Act, which "assumes the UK, including Scotland, is a member of the EU." The devolution legislation requires Holyrood to respect the rules and regulations of EU law. So too must Scottish ministers. "The effect of withdrawal from the EU", he contends, would be to "cass, annul or disable" these provisions - a step which the Lord Advocate concludes "may not, compatibly with the Claim of Right Act 1689, be effected by an act of the prerogative alone."

If the Supreme Court accepted this line of argument, it would be for the Westminster parliament to legislate for Article 50. But where stands Holyrood then? Here, the Lord Advocate's case shifts onto different terrain, and its second main theme. Is Holyrood's consent required or not to legislate for Article 50? As AV Dicey famously maintained, Westminster is sovereign under the British constitution. Between 1707 and 1998, MPs legislated for Scotland. Devolution didn't deprive the UK parliament of this power. This is recognised in the Scotland Act 1998 itself. Section 28(7) stresses that devolution "does not affect the power of the Parliament of the United Kingdom to make laws for Scotland."

But since 1998, the interaction between the two parliaments has been governed by a constitutional convention, sometimes called the Sewel convention. The Scotland Act 2016 recognised the long-standing rule of constitutional morality that Westminster "will not normally legislate with regard to devolved matters without consent." This convention is generally regarded as having two limbs. Firstly, if the UK parliament wants to pass legislation in areas lying within Holyrood's powers - on health say, education, or family law - MPs should seek consent from MSPs. But beyond that, if Westminster legislation would expand or contract the powers of Scottish Parliament or its ministers, this too requires consent. A good example of this was the additional powers devolved by the Scotland Act 2016 itself.

In his brief, the Lord Advocate argues that "withdrawal of the UK form the EU would alter the competence of the Scottish Parliament and Government, and the law applicable in Scotland within devolved competence. A Bill to authorise withdrawal would accordingly engage the legislative consent convention." Holyrood's consent, he says, must be sought.

For the sake of argument, let's say that the UK Supreme Court agree with him. Then what? Does the convention have any legal teeth? Consider, for example, the eminently plausible scenario, that the majority in Holyrood refuses to give its consent to any Article 50 Bill, unless the UK government commits to pursuing the gentlest Brexit possible. Say also that Theresa May is unwilling to bow to this pressure, and presses on with an Article 50 Bill and the hardest of hard Brexits. Is the Lord Advocate seriously suggesting Holyrood has the legal power to frustrate Westminster? In law, does the Scottish Parliament hold a Brexit veto? The answer may disappoint you, and irate headline writers everywhere.

If you read the Scottish Government's submissions carefully, they actually conclude Holyrood has no legal power to "block" an Article 50 Bill passed by Westminster. If the UK parliament were to choose to pass an Act of Parliament without Holyrood's consent, the Lord Advocate concedes, "the courts could not decline to recognise the validity of the resulting Act." He accepts that Holyrood has no legal trump over Brexit. Politically, of course, overriding Holyrood and ignoring its objections would embroil the two governments and parliaments in a potentially poisonous constitutional crisis.

And it is this opportunity to put Theresa May under political pressure which the Lord Advocate seems to be angling for in this intervention. What he is looking for is a direction from the Supreme Court that constitutionally, Holyrood should be consulted about any Article 50 Bill, whether or not Westminster respects Holyrood's conclusions. This, he suggests, "would not involve an impermissible interference with proceedings in Parliament" and would represent the Court fulfilling "its proper function of identifying the constitutional requirements."

We don't yet know how the Attorney-General, for the UK government, might react to the Lord Advocate's submissions here. The Sewel issues were not raised in the Divisional Court, and accordingly, were not discussed by the Lord Chief and his colleagues. But certainly, the government put the word "normally" in the 2016 Act for a reason and you could construct an argument along these lines.

The will of which people? The people of Scotland or the people of England and Wales (or the UK as a whole)? The current position is that the will of the people counts for nothing and parliament must consent to the UK government making the notification set out in Article 50 TEU as part of the process to withdraw the UK from the EU.

It would have been good to have the views of Scotland's judges on record - Court of Session. This was not to be. That's one problem with interventions such as this. Pit nobody in Scotland took a case forward in the way that the claimants Miller and dos Santos have done.

"But alterable by the Parliament of Great-Britain." Notice the critical point here. "At the foundation of the United Kingdom, it was Parliament ... and not the Crown".

Surely the question has to be asked: "who does the UK Parliament answers to?" IF it is her majesty's government[the Parliament of Great-Britain] then ultimately - it can be argued - that it IS the Crown who has the final say. Otherwise what's to stop 'the Crown' creating tiers of government, imposing whatever THEY decide through their 'given' rights - by the Crown - but as a separate entity the 'Crown' cannot be held responsible, despite creating this 'foundation' in the first place.

I slightly disagree with your summary of 86 which is not exhaustive of the possibilities. In addition it's not "and as in your "and would represent the Court fulfilling", it's "to", i.e. relative to the preceding "in this case".

Thanks for this, Andrew. Fascinating that though the political challenge of Brexit is seemingly to the SNP, the constitutional challenge is to the Union itself. Unless "Union" is taken to mean "shut up and do as you're told."

Haven't read the Wolffe opinion but strikes me that withdrawing from the EU doesn't necessarily render unworkable the Scotland Act 1998's requirement that Scotland's devolved competence continue to conform to EU law. I mean, we could pass an Act to say that our law of, say, contract would be the same as, say, the Russian Federation's (to the extent compatible with EU law) without having to be a member of the RF. Another aspect of this is that English common law didn't cease to apply in colonies upon their becoming independent as republics and therefore exiting the British Empire.

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